Recording materials using electron-donating colorless dyes and electron-accepting compounds are already well known as pressure-sensitive papers, heat-sensitive papers, light- and pressure-sensitive papers, electro- and heat-sensitive recording papers, heat-sensitive transfer papers, etc. For example, such recording materials are fully described in British Patent 2,140,449, U.S. Pat. Nos. 4,480,052 and 4,436,920, JP-B-60-23992 (corresponding to U.S. Pat. Nos. 4,181,328) the term "JP-B" as used herein means an "examined Japanese patent publication"), JP-A-57-179836 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-60-123556 and JP-A-60-123557. Particularly, such heat-sensitive recording materials are described in detail in JP-B-43-4160 and JP-B-45-14039. These heat-sensitive recording systems are widely used in the fields of facsimiles, printers, labels, etc. and the practical needs therefor are continually increasing. However, these heat-sensitive recording materials have disadvantages in that fogging is caused by solvents, developed materials are discolored or faded by fats and oils, reagents, etc. Accordingly, the commercial values thereof have been greatly reduced in the fields of labels, slips, word processor paper, plotter paper, etc. in particular. The present inventors have sought to develop practically useful novel recording materials by paying attention to the oil solubility, solubility in water, partition coefficient, pKa, polarity of substituent groups and position of the substituent groups of each of the electron-donating colorless dye and the electron-accepting compound. It has been found, as a general rule, that developed materials which are scarcely fogged by solvents are apt to be faded by fats and oils, reagents, etc., while, on the other hand, developed materials which are scarcely faded by fats and oils, reagents, etc. are apt to be fogged by solvents.
The use of monothiourea compounds for the heat-sensitive recording material are already known in JP-A-59-190893, JP-A-59-176088, JP-A-133096, JP-A-136288 and JP-A-58-222887, but these heat-sensitive recording materials have disadvantages in that fogging and decoloration in the color formed area are caused.